This invention relates to an imporved medical bed in which, in order to reduce the contact pressure between the patient and the bed to thereby protect the patient from bed-sores, a solid particle media in the bed body is fluidized by blowing compressed air into the bed body from below, whereby the patient is made to float over the bed.
The arrangement of a conventional bed of this type and the operating principle of the same will be described with reference to FIGS. 1 and 2. In these figures, reference numeral 1 designates a bed; and 2, a patient lying on the bed 1. The bed 1 comprises a box-shaped bed body 3 which is large enough to allow a patient to lie thereon; and a solid particle media 4 filling the bed body 3, the solid particle media 4 being made up of ceramic pieces having a specific gravity between 2 and 3, and between 50 and 150.mu. in grain size, obtained by coating glass particles with resin. A gap-permeable filter sheet 5 has a mesh smaller than the grain size of the solid particle media 4, and is fixedly secured to the peripheral edge of the bed body 3. A bottom chamber 6 provided on the bottom of the bed body 3, and a porous air diffusing board 7 is disposed between the bottom chamber 6 and the bed body 3.
An air compressor 9 is provided in the rack 8 of the bed; and a compressed-air supplying pipe 10 is connected between the compressor 9 and the bottom chamber 6 through a compressed air blowing mechanism including a radiator 11.
When the compressor 9 is not in operation, the particle media 4 are at rest, and therefore the patient 2 on the bed feels as if he is lying on sand. In this condition, the compressor 9 is operated. As compressed air is supplied through the bottom chamber 6 and the air diffusing board 7 into the bed body 3, the particle media sealed in the bed body 3 by the filter sheet 5 are fluidized by the compressed air spread through the bed body and are ultimately floated. Under this condition, the apparent specific gravity of the particle media 4 is decreased to about 1.1 to 1.2, and the patient is supported while floating over the particle media. In this case, the contact pressure between the particle media and the patient is very low, and therefore the patient feels as if he is floating in air. The compressed air is continuously supplied into the bed body and is discharged into the room through the filter sheet 5. The temperature of the air discharged from the compressor 9 is increased by about 10.degree. to 20.degree. in the compression stroke. Blowing this high temperature air directly beneath the patient may lower the therapeutic effect. In order to eliminate this difficulty, the aforementioned radiator 11 is connected to the pipe 10.
With the medical bed as described above, air is continuously supplied to the bed body while the contact pressure to the patient is being reduced. Accordingly, a good effect can be expected, for instance, for a burned person. Furthermore, a seriously ill patient under medical treatment for a long period who cannot move by himself can be protected from bedsores, because the contact pressure between the patient and the bed is reduced.
In order to seal the particle media 4 within the bed body when fluidized by the operation of the air compressor, it is essential to fixedly secure the filter sheet, which covers the bed body 3, to the peripheral edge of the bed body in a manner such that the filter sheet is in close contact with the peripheral edge. For this purpose, the conventional medical bed as shown in FIGS. 3 through 5, has sheet retaining means comprising a plurality of hand rails 13 which can be readily set on the outer peripheral flange 12 of the bed body 3. The hand rails 13 are fixedly secured to the flange 12 of the bed body 3, in such a manner that the sheet 5 is held between the flange 12 and the hand rails 13 and is in close contact with the flange 12 through a retaining packing 14.
Heretofore, in order to secure the hand rails 13 to the bed body 3, a plurality of bolts 15 were embedded in the lower surface of each hand rail 13 at suitable intervals, as shown in FIG. 4, while bolt inserting holes were cut in the sheet 5 and in the flange of the bed body 3. The bolts were then inserted into the holes in the sheet and the flange to retain the sheet 5 from above by the hand rails as shown in FIG. 3, and knurled knobs 16 were screwed onto the bolts thus inserted, to fixedly secure the sheet to the bed body 3. Twenty to thirty bolts 15 were arranged on the flange of the bed body, and therefore, required a relatively long period of time, and was troublesome. If the bolts are not sufficiently tightened, the particle media is blown from the bed. This changing operation must be carried out whenever the sheet becomes dirty, and is generally conducted by nurses. Accordingly, it is desirable that the sheet fixing work be readily achievable even by unskilled persons.